The on-board electrical system of a vehicle connects a power source via distributors and sub-distributors to the various loads or consumers. Thus, the components of the on-board electrical systems may be understood to include distributors, sub-distributors and loads, as well as cables connecting these elements together. The cables in such cases are connected via plug connections to interfaces of the distributors, sub-distributors or loads. The plug connections represent inputs and outputs of the given components. Aside from a total failure of a cable, degradation processes may befall the cables and plug connections in the course of the lifetime of a vehicle. These processes cause a gradual deterioration of the affected components of the on-board electrical system and ultimately bring about the failure of the component.
The electrification of growing numbers of functions has been accompanied by steadily increasing numbers of consumers in the system. The task of safeguarding the on-board electrical system as an energetically and informationally linked system is becoming increasingly complex as possible interactions of the components become more and more difficult to recognize. At the same time, a comprehensive diagnostic program should be implemented in the on-board system in order to meet requirements concerning functional safety.
Safety-relevant functions such as automated steering during parallel parking already exist in today's vehicles. These functions must be fail-safe, meaning that when an error is detected the safe state “off” is adopted and the driver is informed via display instruments. Observing the functional safety of these functions therefore often ends at the plug of the control device, since an interruption or outage of the power supply leads directly to the safe state “off”. Thus, there is no need for a safety function at the power supply level.
Automated driving systems on the other hand must be configured fail operational with an error state transition to the safe state “on”. The power supply outage (supply line) or communication (bus line) outage for this function may result in a direct endangerment of human beings. The safe “on” state must be maintained until the vehicle can be halted at a safe location or until the driver can take over control of the vehicle.
DE 10 2015 209 588 B3 discloses a simple and reliable device for recognizing malfunctions in an on-board electrical system. The device includes a receiving unit configured to receive a first and a second sequence of measured values, with the measured values of the first sequence being measured at a first measuring point of the on-board electrical system and with the measured values of the second sequence being measured at a second measuring point of the on-board electrical system that differs from the first measuring point. The measured values represent current or voltage values. The device also includes an evaluation unit configured to recognize the occurrence of a malfunction on the basis of a comparison of a first dispersion of the measured values of the first sequence and a second dispersion of the measured values of the second sequence.
DE 10 2014 018 640 B3 discloses a method for detecting electrical resistance in a motor vehicle. In a first measuring phase, in which a first device receives a load current from a voltage source and all other devices receive a quiescent current from the voltage source, the first device detects a first voltage value and a load current value and a second device detects a second voltage value. In a second measuring phase in which each of the devices receives a particular quiescent current from the voltage source, the second device detects a third voltage value and the first device a fourth voltage value. An evaluating unit ascertains a connection resistance of a connecting cable of the first device on the basis of the first voltage value, the second voltage value, the third voltage value, the fourth voltage value and the load current value.
DE 10 2014 004 791 B3 describes a method of checking a connection between a battery that supplies a low-voltage network of a motor vehicle and the low-voltage network. In this method, a DC voltage converter connects a high-voltage network to the low-voltage network, and the output voltage is modulated by the DC voltage converter into the low-voltage network at a modulation frequency. The current thereby injected and the voltage thereby injected are measured by the battery and a resistance value is determined and evaluated with regard to at least one connection criterion. A disruption of the connection is then ascertained if there is at least one unfulfilled connection criterion.